1. Field of the Invention
The present invention relates generally to a microwave plasma processing system which is designed to produce plasma in a processing vessel by microwaves introduced from an antenna. More specifically, the invention relates to the improvement of a wave guiding structure of the antenna.
2. Description of the Related Art
FIG. 5 shows an example of a conventional microwave plasma processing system. The microwave plasma processing system shown in FIG. 5 comprises a processing vessel 1 having a transmission window 10 capable of transmitting microwaves. On the top of the transmission window 10 of the processing vessel 1, a microwave antenna 102 is mounted.
The antenna 102 serves as a thin cylindrical waveguide, and the bottom thereof is formed with a plurality of slots 106 which are appropriately distributed. The central portion of the antenna 102 is connected to a coaxial line 104. The coaxial line 104 comprises an inner conductor 104a and an outer conductor 104b. Through the coaxial line 104, microwaves are supplied to the antenna 102 from a microwave supply source (not shown).
The microwaves supplied to the antenna 102 through the coaxial line 104 are radiated downwards from the slots 106 while being propagated outwardly in radial directions from the central portion of the antenna 102. When the microwaves reflect on the outer peripheral portion of the antenna 102 to be returned, the microwaves traveling outwardly and inwardly in radial directions interfere with each other to produce standing waves.
The microwave plasma processing system shown in FIG. 5 comprises a supporting table 12 provided on the bottom of the processing vessel 1. In the bottom of the processing vessel 1 corresponding to the surrounding of the supporting table 12, an exhaust port 13 for evacuating the interior of the processing vessel 1 is formed. At an appropriate position in the upper portion of the processing container 1, an introducing pipe 14 for introducing a process gas or the like is provided.
The microwave plasma processing system is designed to produce the plasma of the process gas with microwaves, which are introduced from (the slots 106 of) the antenna 102, in the processing vessel 1 which is held at a predetermined degree of vacuum. With the produced plasma, various intended plasma processes, such as deposition or etching processes, can be carried out with respect to an object W to be processed (e.g., a semiconductor wafer or a LDC substrate) on the supporting table 12.
In the above-described microwave plasma processing system, there is the following problem. That is, because of the structure that microwaves are radially propagated in the antenna 102, the radial distribution of the microwaves introduced into the processing vessel 1 from the antenna 102 is difficult to be uniform. For that reason, there is a problem in that the uniformity of the plasma processing for the object W to be processed in the processing vessel 1 decreases.
In accordance with processing conditions, there are some cases where it is not the best to simply obtain the radially uniform intensity of microwaves in the antenna 102 in order to improve the uniformity of the plasma process with respect to the object W to be processed. In such cases, it is required that the radial distribution of microwaves introduced into the processing vessel from the antenna can be optimally set in accordance with processing conditions.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a microwave plasma processing system capable of optimally setting the radial distribution of microwaves, which are introduced into a processing vessel from an antenna, in accordance with processing conditions.
In order to accomplish the aforementioned and other objects, according to the present invention, there is provided a microwave plasma processing system comprising: a processing vessel; an antenna for introducing microwaves into the processing vessel; a microwave supply source for supplying the microwaves to the antenna; and a connecting waveguide for connecting the microwave supply source to the antenna, wherein a plasma is produced in the processing vessel by the microwaves introduced from the antenna, the antenna having a plurality of substantially ring-shaped antenna waveguides which are substantially concentrically arranged, each of the antenna waveguides comprising a rectangular waveguide having a wall in which a plurality of slots are formed at intervals, the proximal end portion of each of the antenna waveguides being connected to the connecting waveguide.
According to the present invention, there is also provided a microwave plasma processing system comprising: a processing vessel having a microwave transmittable top wall; an antenna mounted on the top wall of the processing vessel; a microwave supply source for supplying said microwaves to the antenna; and a connecting waveguide for connecting the microwave supply source to the antenna, wherein a plasma is produced in the processing vessel by the microwaves introduced from the antenna, the antenna having a plurality of substantially ring-shaped antenna waveguides which are substantially concentrically arranged, each of the antenna waveguides comprising a rectangular waveguide having a bottom wall in which a plurality of slots are formed at intervals, the proximal end portion of each of the antenna waveguides being connected to the connecting waveguide.
According to these plasma processing systems, it is possible to change the intensity of microwaves by adjusting the dimension of the cross section of each of the antenna waveguides and adjusting the dimension of each of the slots and the interval between adjacent slots every antenna waveguide. Therefore, the radial distribution of microwaves introduced into the processing vessel from the antenna can be optimally set in accordance with processing conditions. Thus, for example, it is possible to remarkably improve the uniformity of a plasma process in the processing vessel.
In the above-described plasma processing systems, at least one of the antenna waveguides of the antenna is preferably provided with aperture variable device for varying the size of an aperture at the proximal end portion. Thus, the intensity of microwaves distributed to a corresponding one of the antenna waveguides can be adjusted by varying the dimension of the aperture in the proximal end portion of the corresponding antenna waveguide by the aperture variable device. Therefore, the radial distribution of microwaves introduced into the processing vessel from the antenna can be freely changed in accordance with the variation in process conditions.
The terminal end portion of each of the antenna waveguides of the antenna may be closed with a conductor or a microwave absorber.
The connecting waveguide may extend to the proximal end portion of the innermost one of the antenna waveguides in a substantially radial direction with respect to each of the antenna waveguides. In such a case, the terminal end portion of the connecting waveguide may be closed with a conductor or a microwave absorber.